The present application relates to a serial optical transport networks based on multimode/multicore fibers.
The optical communication systems have been rapidly evolving recently in order to meet continuously increasing demands on transmission capacity, originating mostly from the Internet and multimedia applications. In order to satisfy high capacity demands, according to some industry experts, the 1 TbE standard should be completed in several years. Coherent optical OFDM is one possible pathway towards achieving multi-Tb/s optical transport. Another approach is based on multidimensional coded modulation. Namely, by increasing the number of dimensions (i.e., the number of orthonormal basis functions), a system can increase the aggregate data rate of the system without degrading the bit error rate (BER) performance as long as orthogonality among basis functions is preserved. Most of the papers on multidimensional signal constellations for optical communications so far have been related to single carrier and SMF-based systems.
The MMF is traditionally considered as the medium for short-reach applications. However, one recent experiment, in which 21.4 Gb/s polarization-multiplexed coherent OFDM transmission over 200 km of MMF has been demonstrated, indicates that MMFs can be used for metro and medium-haul applications, as well. Today's MMFs are however far away from being a medium suitable for long-haul transmission. The main issues are related to high loss and excessive number of modes that overwhelms the computational capabilities of currently existing silicon chips. Interestingly enough, the theory behind dual-mode optical fiber is well developed. For example, the group delay experiences a difference between LP01 and LP11 modes vanishes at the normalized frequency of V0=6.8, which is just below the cutoff frequency of the third mode. The corresponding core diameter and the refractive index difference at λ=1380 nm are 24.8 μm and Δ=(n12−n22)/2n12=0.3% [where n1 (n2) is the refractive index of the core (cladding)], respectively. The similar approach is applicable to few-mode fibers.